Protein, phosphorus, and energy utilization in young chickens and pigs as affected by microbial phytase and nutritionally-enhanced corn hybrids

Experiments were conducted to evaluate the efficacy of phytase for improving protein-amino acid (AA) utilization in corn gluten meal (CGM) and soybean meal (SBM) for young chickens and pigs using slope-ratio growth, protein accretion, and protein efficiency ratio (g weight gain/g protein intake) assays. Regardless of evaluation method, microbial phytase did not (P > 0.10) affect protein-AA utilization in CGM or SBM for young chickens and pigs, and this inability was not (P > 0.10) altered by dietary excesses of calcium and available phosphorus (P). Also, it was determined that phytase-mediated responses in chicks fed AA- and P-deficient diets were due solely to increased P utilization and not to improved AA utilization. Reducing inorganic P and selected trace-mineral supplementation of late-finishing swine diets did not (P > 0.10) adversely affect growth performance and carcass traits, but resulted in depressed (P < 0.05) bone strength, which was ameliorated (P > 0.05) with phytase supplementation. Low-phytate (LP) corn was found to contain two times more (P < 0.05) bioavailable P than conventional corn (CONV), and employing LP-corn and microbial phytase, or both, effectively reduced (P < 0.05) the need for inorganic P supplementation, and ultimately reduced (P < 0.05) P excretion by chicks. Moreover, the P bioavailability advantage in LP-corn over CONV-corn translated to more (P < 0.05) bioavailable P in corn gluten feed (CGF) derived from LP-corn compared to that derived from CONV-corn. The most problematic and perplexing observation was the reduced metabolizable energy in corn hybrids containing reduced phytic acid levels. Incorporating the low-phytate trait in either CONV (LP) or in a high protein-high oil hybrid (HPO/LP) reduced the energy value for chickens compared to CONV and HPO controls; it also decreased the energy value of HPO/LP for pigs compared to HPO. These data demonstrate the need for comprehensive evaluation of nutritionally-enhanced grain varieties.